Can my 64-year-old dad retire soon? $700k assets + Social Security

I'm trying to help my dad figure out when he can realistically retire and how to handle an upcoming inheritance. I've been crunching the numbers, but I'd like some outside opinions.

Current situation:

• Dad is 64 and makes about $180k/year
• About $300k in his 401(k), currently invested in SPY/S&P 500 adjacent fund
• Receiving approximately $400k inheritance
• Mom already receives $1,300/month Social Security

• Dad's Social Security estimates:

  • Now: ~$2,800/month
  • Age 67 (FRA): $3,708/month
  • Age 70: ~$4,768/month

• House is worth roughly $400k-$500k

• About $300k left on a ~3% mortgage

• Total house payment with taxes and insurance is about $1,700/month

• Mom has an illness that results in fairly high ongoing out-of-pocket medical expenses

My main goal is figuring out whether Dad can comfortably retire sooner rather than just automatically working until 67.

One idea I've been considering is:

• Move the $300k 401(k) into a bond index fund
• Invest most of the $400k inheritance into SPY in taxable
• This would give them roughly a 57/43 stock/bond portfolio
• Potentially retire before 67 and use the portfolio as a bridge while delaying Dad's Social Security until 67 or possibly 70

I'm also wondering whether they should just keep the cheap 3% mortgage rather than paying it off.

Main questions:

• Does retiring around 64-65 seem realistic, or should he work until 67?
• Would you claim Social Security at 67 or use investments to bridge to 70?
• How would you allocate the $300k 401(k) and $400k inheritance?
• Does bonds in the 401(k) + equities in taxable make sense?
• Would you keep the 3% mortgage?
• Anything important I'm overlooking?

I know I still need to get a better handle on their total annual spending and medical expenses, but I'm mainly trying to help my dad figure out whether he's reached the point where continuing to work is optional rather than necessary but I'd estimate their spending is $80k a year.